This invention relates to a vehicle navigation system and a recording medium for execution of a route search to identify a guidance route from a departing point or the present position of a vehicle to a destination, and which provides route guidance for the identified guidance route.
Vehicle navigation systems search for a route from a departing point or the present position of the vehicle to the designated destination and provide route guidance for the thus identified "guidance route." To accomplish this, the vehicle navigation system has a functional capability allowing the driver to designate a road preference and provides for search for a route including the designated road. In addition, some navigation systems allow for selection of a desired road from a list of the roads traversing the entire country and for search of a route with the selected road given priority. Further, some navigation systems operate to search for the shortest distance route, the shortest time route, or the minimum cost (weighted) route and to display respective routes distinguished from each other (see, for example, Japanese Patent Publication No. 130299/89).
In a conventional system which searches for a route by giving priority to main roads, i.e., roads of wide width, routes passing through relatively congested city areas are likely to be included in the search. This results in a problem with the quality of the identified "guidance route" in that the travel time for the vehicle may be excessively long relative to the distance of the route.
Further, some of the conventional systems have a functional capability allowing for designating a road to be avoided; however, this capability complicates their operation since these systems require designation of a road that the driver desires to avoid for every route search. When the route from a starting point to a destination is long, the number of the roads to be selected tends to be huge and the selection operation becomes very difficult. Even if the roads to be selected are classified as highways, toll ways, interstates, local roads, etc., still each road classification contains a huge number of roads. As a result, a difficulty arises in that several operations taking into account classification and hierarchy are required to designate a road the driver desires to avoid and this complicates operation of the system. Further, in the case where the road to be designated has no name or the name of the road is unknown, the system can't select a road.